Choosing And Using Guiding Catheters Health And Social Care Essay

Guiding catheters (otherwise known as guide catheters) are the conduit tubing by which percutaneous coronary interventions (PCIs) are performed. Choosing an appropriate guiding catheter is a deliberate action undertaken upon the target vessel at the onset of PCI and a miscalculation at this step may be setting the stage for an unsuccessful PCI attempt. In the worst-case but not uncommon scenario, inappropriately selecting an aggressively-curved guiding catheter may induce a major complication such as ostial coronary dissection within seconds of intubating the target vessel! On the other hand, stability of the chosen guide catheter throughout the case is paramount to any successful PCI attempt.

Apart from providing access to the ostium of the target vessel for delivery of interventional devices, guiding catheters serve three other functions. As with coronary angiography, contrast is selectively delivered to the coronary artery intubated; however, opacification is greater than with diagnostic catheters in view of the larger internal lumen and therefore better profiles the coronary lesion(s), sometimes prompting a change in PCI strategy when the lesion(s) appear more/less severe than indicated in the original diagnostic angiogram.

Thirdly, the guiding catheter provides mechanical support to allow passage of the interventional kit to and past the coronary lesion(s) with subsequent deployment of balloons/stents at the lesion site. The support provided by a guiding catheter can be described as either active or passive. Passive support is due to a guiding catheter’s inherent stiffness, conformity to the aortic root curvature and degree of co-axial alignment of the distal tip within the intubated coronary artery. When using a guiding catheter in a passive mode, additional manipulation is generally not required for advancement/deployment of interventional devices. If passive support is inadequate, then active support can be achieved either by manipulating the guiding catheter so that the aortic root provides “backup” or by deep sub-selective advancement of the guiding catheter into the coronary vessel.

Finally, assessment of coronary arterial pressure at the tip of the guiding catheter is possible since the fluid-filled lumen is in continuity (in between contrast injections) with a manifold connected to an external pressure transducer, as with diagnostic coronary angiography.

23.2.1 Design features of guiding catheters

A multitude of factors need to be considered in guiding catheter design. These include catheter size (maximising internal diameter whilst minimising wall diameter), radial strength (to minimize “kinking”), minimising internal frictional resistance, columnar and torsional strength (to maximise “pushability” and “torquability”), overall flexibility and radiodensity. The main difference in function between diagnostic versus guiding catheters is the latter’s need for providing support and passage for interventional devices hence the difference in design features as summarized in Table 23.2.1.

There may be a trade-off in order to achieve the desired balance of characteristics. For a given external diameter, increasing lumen diameter can only be achieved by reducing wall thickness, yet overall attributes may be preserved by utilising different wall material and construction as claimed by manufacturers of different brands of guiding catheters. More flexible catheters should be safer to manipulate into active engagement yet a stiffer catheter should provide better passive support and potentially obviate the need for active support. Therefore a design compromise often utilised is to design the distal portion of the guiding catheter to be softer and more flexible while retaining strength and stiffness in the main proximal portion of the catheter.

Table 23.2.1 Comparison of diagnostic versus guiding coronary catheters

Diagnostic catheters

Guiding catheters

Range of sizes available: 4F –

Range of sizes available: 5F –

Wall constructed in two-layers

Wall constructed in 3 layers generally

Thicker wall diameter yet less radial strength

Thinner wall diameter yet greater radial strength

Smaller internal diameter/narrower lumen

Larger internal diameter/wider lumen

Lesser transmission of rotational torque

Greater transmission of rotational torque

No radio-opaque tip marker

Radio-opaque tip marker present

Longer tip

Shorter tip

Angulated primary (most distal) curve

23.2.2 Size of guiding catheter

Selection of guiding catheter size is generally determined by the size/profile of interventional devices anticipated to be used during the procedure (e.g. straightforward PCI balloons/stents would not necessitate as large a guiding catheter internal lumen as PCI involving “kissing balloon” technique or rotational atherectomy). In keeping with all vascular devices, size is described in terms of external diameter whereby 1 French (Fr) = 0.33cm. In general, straightforward PCI is conducted using 6Fr guiding catheters whereas the more complicated procedures described may require 7Fr or 8Fr catheters undertaken usually via the transfemoral route.

However, increasingly transradial access is being utilised for PCI as it has less associated vascular complications (e.g. puncture site or retroperitoneal haemorrhage), allows for earlier patient mobilisation post-procedure and has overall better patient satisfaction (references!) as compared to transfemoral access. Disadvantages of transradial PCI tend to relate to the limitation of guiding catheter size imposed upon by the radial artery’s smaller diameter as compared to the femoral artery, especially if the smaller calibre results in inability to complete the whole procedure via this route due to radial artery spasm; however, with transradial access there is rarely any post-procedure complication of any clinical consequence including early/late thrombosis of the radial artery (up to 5% incidence- reference).

Until recently the size of guiding catheter could at most be equal to that of the access sheath size i.e. if it is only possible to insert a 5Fr sheath into a small calibre radial artery then a 5Fr guiding catheter would be the largest to fit such a sheath. A modern option has been the advent of “sheathless” guiding catheters, whereby as the name suggests a guiding catheter may be inserted without a vascular access sheath. Sheathless guiding catheters with an outer diameter approximately 1.5F size smaller than the corresponding radial artery sheath overcomes this limitation with a high success rate (reference).

Regardless of access route complications, the main advantages of using as small a guiding catheter as possible to complete a successful PCI include less potential for occlusive intubation of the target vessel ostium but deeper intubation if increased active guide support is required. Conversely smaller Fr guiding catheters provide less passive support and sometimes may require the added complexity of upsizing to a larger diameter if more bulky interventional devices become necessary during the PCI, which is especially not ideal in the emergency/ bail-out setting.

23.2.3 Shape of guiding catheter

Guiding catheters are available in a variety of pre-formed shapes designed to conform to specific aortic arch/root and coronary anatomy. As shown in Figure 23.2.1(figure needed), a guiding catheter can be described in terms of the configuration of its primary, secondary and (if present) tertiary curves. By convention, the numerical value assigned to each catheter is a measurement of the distance between the primary and secondary curves of the catheter, where a higher number denotes a more open configuration.

The most commonly used diagnostic catheters for coronary angiography are the Judkins left and right configuration catheters, and their guiding catheter counterparts are equally popular for PCI (see Figure 23.2.2, figure needed). Judkins catheters are available in a range of sizes, from 3cm to 6cm. As alluded to in Table 3.1.9.1, a Judkins guiding catheter has a shortened distal tip and more open primary curve as compared to a Judkins diagnostic catheter, a design feature which improves the coaxial relationship of the tip of the guiding catheter within the coronary ostium and hence reduces the potential for coronary trauma.

Other popular guiding catheter shapes include the Amplatz configurations, which provide a greater degree of passive support when seated, but tend to engage the coronary vessel more aggressively than their Judkins counterparts with consequent increased risk of causing coronary/aortic dissection. However in patients with a superior coronary origin in particular, Amplatz catheters often provide more coaxial coronary engagement and better support due to their conformity to the aortic root curvature (see Figure 23.2.3, figure needed).

In general, the interventionalist’s approach is to choose a guiding catheter shape appropriate to the anatomy to achieve engagement in the most coaxial manner, and rely upon passive support for the advancement of interventional devices. However, when treating Type C lesions (e.g. severe calcific stenoses, lengthy lesions in tortuous vessels, or chronic total occlusions ), guiding catheter manipulation to create active support may be required as previously alluded to. With the guiding catheter already engaged, the method to achieve active support by deep subselective engagement is to push the catheter tip over an undeployed angioplasty balloon in the proximal vessel or “pull” it in over the guidewire when the angioplasty balloon is inflated. Prior to this manoeuvre, it is important to firstly gauge the orientation of the guiding catheter tip within the proximal vessel segment: in the case of the RCA, this is usually best visualised in the right anterior oblique (RAO) projection with clockwise rotation of the guiding catheter being usually needed to achieve coaxial alignment.

Alternatively if a Judkins-type catheter is in-situ, then manipulation of the guiding catheter into a shape that conforms to the aortic root is another method of active engagement termed “Amplatzing”. This change in configuration can be induced with both Judkins left and right guiding catheters. In the case of the Judkins left guiding catheter, the manoeuvre is performed by advancing the guiding catheter over a deployed angioplasty balloon whilst applying counterclockwise torque, with simultaneous retraction of the balloon catheter: the guiding catheter tip should then prolapse upward into the left mainstem while the secondary curve becomes bent into the left coronary cusp, assuming an Amplatz-like shape.(?illustration)

Potential acute complications of both methods of active engagement include intimal trauma causing coronary dissection and/or occlusion of the artery. A later complication thought to be related to guiding catheter tip trauma is rapid progression of coronary stenosis, which has been described with left mainstem disease.

23.2.4 Other varieties of guiding catheter

Side-hole catheters

Some conventional guiding catheters have a variation available with a side-hole at the tip to allow additional passage of blood to the intubated coronary artery, when there is deemed to be insufficient space between the outer wall of the guiding catheter and the inner lumen of the intubated coronary to allow for adequate coronary perfusion. One disadvantage of side-holes is the slight reduction in vessel opacification during contrast injections due to some of the contrast escaping via the side-holes. The main disadvantage is that there may still be inadequate end-bed coronary perfusion but yet the appearance of a normal pressure tracing derived from side-hole flow, and therefore many interventionalists do not perceive that benefit is derived from the use of side-hole catheters.

“Mother-and-child” guiding catheters

Aggressive guiding catheter support and other angioplasty techniques may fail to negotiate passage of interventional devices to the target lesion in complex coronary anatomy. A recent development to surmount this challenge has been the advent of “mother-and-child” guiding catheters. It essentially involves telescoping a specifically designed longer length but smaller sized (“child” e.g. 5F) guiding catheter into a larger sized (“mother” e.g. 6F) standard guiding catheter so that the tip of the “child” catheter protrudes beyond the “mother” catheter and effectively deeply intubates the target vessel to allow delivery of a stent.

The Heartrail II® (Terumo, Japan) is one such system, using the target vessel itself to provide the extra backup support required for stent delivery. The absence of a primary curve and the flexibility of its tip permit the “child” catheter to remain coaxial within the target vessel, aiming to reduce the risk of catheter-induced coronary dissection. The Guideliner ® (Vascular Solutions Inc, Minneapolis, USA) is a variation upon the theme: it is a “child” catheter extension delivered through a standard guiding catheter on a monorail. It comprises a flexible 20 cm straight extension (internal diameter approximately one Fr size smaller than the guiding catheter) connected to a stainless-steel push tube, with a “collar” that can be deployed through the existing Y-adapter for rapid exchange delivery. The extension comprises an inner polytetrafluoroethylene (PTFE: Teflon) lining, surrounded by a stainless-steel coil (to impartsflexibility and strength) and an outer layer of Pebax® polymer. The quoted internal lumen diameters of both systems are shown in Table 23.2.2. The smallest “child” catheter available is a 4 Fr Kiwami ® ST01 “child” catheter developed by Terumo which is lower profile, has a more flexible shaft and an additional hydrophilic coating allowing for easier deep engagement.

Table 23.2.2 Comparison of internal diameter for Heartrail® and Guideliner® “child” catheters

Sizes available

Heartrail® internal diameter

Guideliner® internal diameter

0.059 inch

0.056 inch

0.071 inch

0.062 inch

0.081 inch

0.071

Apart from risk of coronary dissection from deep engagement, a potential increased complication of the “mother-and-child” systems is air embolism- this can occur when the “child” catheter is wedged against the vessel wall. Methods to avoid air embolism in this context include careful attention to the pressure tracing displayed and checking there is backflow of blood from the manifold’s Y-connector after stent deployment.

Tornus guiding catheter

?talk about normal coronary artery origin/angles

(will talk about dilated aortic root/ascending aorta when describing different JL sizes for LCA guide caths)

23.2.5 Guiding catheter selection strategies

Selection of an appropriate guiding catheter for any interventional procedure is of paramount importance to the successful completion of the case without complications. Apart from the issue of size as discussed above, choice of an appropriate variety of guiding catheter is based upon

diagnostic catheter used for the original diagnostic angiogram

route of access (radial vs femoral)

size and shape of the ascending aorta and aortic arch

target vessel characteristics

target lesion characteristics

type of interventional devices planned for the procedure (e.g. rotational atherectomy)

It is always useful to review the characteristics of the original diagnostic catheter in terms of whether its shape and size provided good stability and orientation during the diagnostic angiogram. Generally-speaking, if for example a JL4 diagnostic catheter appeared to be an appropriate fit, then ½ Fr size smaller guiding catheter (i.e. JL3.5 ) would provide a corresponding fit. However, if route of access has changed between diagnostic and interventional procedures (e.g. from radial to femoral or vice-versa) then this equation will not hold true and a given shape may provide inadequate support for device deployment compared to the minimal support required for selective coronary angiography, necessitating selection of a more aggressive guiding catheter. At any rate, the influence of size and curvature of the ascending aorta/aortic arch upon the behaviour of the diagnostic catheter should help predict the behaviour of a similarly shaped guiding catheter.

For a given target vessel, the presence/absence of significant atheroma and geometrical orientation of the proximal coronary segment is a major factor determining the choice of guiding catheter, as is the presence/absence of significant vessel calcification. Target lesion variables needing to be taken into account include number of lesions to treat, lesion severity (especially chronic vs acute nature of any occlusion), lesion length, location of lesions to be treated (especially if side-branches require protection or treatment with “kissing balloon” techniques) and vessel tortuosity proximal to the target lesion(s). In general, treatment of coronary chronic total occlusions requires a guiding catheter with good backup/support whereas for rotational atherectomy it is more important for the guiding catheter to be coaxial than provide good backup.

The following sections endeavour to outline these considerations in selecting and manipulating guiding catheters for left and right coronary arteries, vein grafts and internal mammary grafts.

Left coronary artery

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